Integrated circuit (IC) devices are often fabricated in large numbers on a semiconductor substrate, such as a semiconductor wafer. Once fabrication is completed, the semiconductor substrate (e.g., wafer) is cut so that the individual IC devices are singulated into individual dies with each die including an IC device. For example, a large number of microcontroller IC devices can be fabricated on a semiconductor wafer and then singulated into individual dies with each die having one of the microcontroller IC devices. Once singulated, the dies are often included within an IC package. One technique for providing electrical connections to dies within a semiconductor device packages is through the use of lead frames.
A wide variety of lead frame implementations have been used. In general, a lead frame can be thought of as a mechanical support structure for the die within the IC package that also provides electrical connections to and from the die. A lead frame will typically include a die-attach area where the die is attached to the lead frame, and the lead frame will typically include one or more lead fingers and may also include a down-bond area. The lead fingers are often utilized to provide electrical connections between the die and circuitry that will be external to the semiconductor package. Down-bond areas are often used for connections that are internal to the semiconductor package. In some lead frame solutions, a wire bonding process is used to attach wires from the lead fingers and/or down-bond areas to bond pads and/or sites on the die. If desired, other electrical connection techniques can also be used (e.g., solder bumps). The lead frame and die assembly, including electrical connections, are ultimately mounted within a completed IC package. Further, for some IC packages, multiple dies may be included using one or more lead frames to facilitate mechanical support and electrical connections. Still further, it is noted that lead frames can be encapsulated in no-lead packages that have no external leads.
Lead frames are often provided by lead frame manufacturers to another assembler or manufacturer who then attaches dies to the lead frames and adds electrical connections, such as through a wire bonding process. To help improve the electrical connections that will ultimately be made between the die and the lead frame, lead frame manufacturers typically add metal plating to lead fingers and down-bond areas on the lead frames. This metal plating can use a variety of metals, and gold and/or silver plating is a common technique. As such, the lead frame will typically be pre-plated with gold, silver, and/or another metal when the lead frame is provided to the entity that performs the die attachment.
FIG. 1 (Prior Art) is a block diagram of an embodiment 100 representing a pre-plated lead frame. The pre-plated lead frame embodiment 100 depicted includes a lead frame support structure 102, which further includes a die-attach area 104. A plurality of lead fingers 108 are also coupled to the lead frame support structure 102. Further, the block 106 represents a down-bond area where a down-bond connection will later be made. As described above and represented by the “P” labels in embodiment 100, the lead fingers 108 and the down-bond area 106 have been pre-plated (e.g., gold plating, silver plating) to improve later electrical connections that will be made after die attachment.
FIG. 2 (Prior Art) is an embodiment 200 of a side-view of the pre-plated lead frame of FIG. 1 (Prior Art). For the embodiment 200 depicted, lead fingers 108 include a base material 202 and a plating material 204. The down-bond area 106 can include the same plating material 204. For example, gold plating or silver plating can be used to form the plating material 204. The completed lead frame, therefore, includes pre-plating of the expected electrical connection points, such as lead fingers 108 and down-bond area 106, that will be used after die-attach processing for making electrical connections.
FIG. 3 (Prior Art) is an embodiment 300 for example materials within a pre-plated portion of a lead frame. For the embodiment 300 depicted, the underlying support material for the lead frame is a copper (Cu) alloy 302. To pre-plate areas of interest for the lead frame, such as lead fingers 108 and down-bond area 106, additional metal layers are provided, such as layers 304 and 306, followed by a final metal plating layer 308. As depicted, nickel (Ni) is used for metal layer 304. Palladium (Pd) is used for metal layer 306. And gold (Au) is used for the final pre-plating metal layer 308. Silver (Ag) or another desired material could also be utilized as the final pre-plating metal layer 308, if desired.
While metal plating areas of interest on pre-plated lead frames, such as pre-plated lead fingers and pre-plated down-bond areas, can provided improved electrical connections, any anomalies and associated defects (e.g., delaminating of metal plating, non-stick of metal plating on lead, contamination of metal plating areas, or other defects) associated with these pre-plated areas of interest can cause device performance degradation or failure.